Controlling Registration Floods In VoIP Networks Via DNS

ABSTRACT

A mechanism controls global synchronization, or registration floods, that may result when a large number of endpoints in a Voice over Internet Protocol (VoIP) network such as an Internet Protocol Multimedia Subsystem (IMS) come online simultaneously after a catastrophic failure. The mechanism allows the Domain Name System (DNS) infrastructure to efficiently control the overload condition by registering user end points with backup border elements, and by staggering and by randomizing the time-to-live (TTL) parameter in registrations with backup border elements.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/589,235, entitled “Controlling Registration Floods in VoIPNetworks via DNS,” filed on Oct. 20, 2009, the disclosure of which isincorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present invention relates generally to Voice over Internet Protocol(VoIP) networks. More particularly, the present application relates tomethods and systems for recovering from a catastrophic failure thatresults in a larger number of endpoints coming on line simultaneouslyafter the VoIP network is restored.

BACKGROUND

A simplified call flow for registration of user endpoint devices isillustrated by the sequence diagram 100 shown in FIG. 1. The timelineillustrates the messaging typically used in registering a user endpointdevice (UE) 110 with a VoIP network 130 such as a Next GenerationNetwork (NGN).

To prepare for registration, the UE 110 transmits two levels of DomainName System (DNS) queries to a DNS server. First, an SRV query 151against a high-level Fully Qualified Domain Name (FQDN) is transmittedto a DNS server 124. One or more FQDNs are returned in a response 152;the FQDNs corresponding to specific border elements of the VoIP network.A second DNS A query 153 is then transmitted to determine the IPaddresses of those FQDNs. The IP addresses are returned at 154 from theDNS server 124 to the UE 110.

The UE 110 then registers via a border element 132 such as a SessionBorder Controller (SBC) in the VoIP network 130, by transmitting aSession Initiation Protocol (SIP) registration request 155 to the borderelement 132. The registration request includes at least one InternetProtocol (IP) address of a FQDN. The border element 132, in turn,registers with a registrar 134 on behalf of the VoIP user endpoint 110by forwarding the registration request at 156. The registrar 134 thenpopulates a local registration cache.

During recovery from a catastrophic failure such as a wide-scale poweroutage, a large number of VoIP endpoints such as UE 110 may come onlinesimultaneously. A VoIP network can easily become overwhelmed when allendpoints attempt to come online simultaneously. In an environment basedon SIP, the endpoints will all issue SIP REGISTER registration requests155 within a small window of time. A large percentage of those REGISTERmessages will fail with a SIP error or timeout as a result of theoverload. The endpoints may re-transmit in a timeout scenario or theymay attempt to re-register in an error scenario. In either case, thetimers in the endpoints that control this process will, for the mostpart, be the same and the global synchronization attempts and failureswill continue. Furthermore, the VoIP infrastructure may becomeoverwhelmed and even calls from registered endpoints may fail.

A backoff scheme has been proposed to address the above problems,wherein a backoff algorithm is incorporated into the VoIP user endpoints110. That approach, however, is very static in nature. A given VoIPendpoint does not know whether a failure impacts itself or manyendpoints, how many endpoints are affected, and at what rate the networkcan allow them to come back online.

Solutions implemented at the VoIP border element 132 have also beenconsidered. In those solutions, the border elements must still processthe message flood, while gracefully rejecting some of the requests.

There therefore remains a need for a method and system capable ofquickly and automatically reinstating a VoIP communications system aftera catastrophic failure. The technique should re-register user endpointsas quickly as possible without overwhelming the VoIP network.

SUMMARY

The present invention addresses the needs described above by providing amethod for registering a multimedia endpoint via a border element in amultimedia network. At a DNS server in the multimedia network, a DNSquery is received from the multimedia endpoint, the query containing anidentifier of the end point and requesting an address of a borderelement for use in registering for a multimedia service. Based on theidentifier of the end point, a primary border element associated withthe end point is determined. If a volume of DNS queries from end pointsassociated with the primary border element is below a threshold capacityof the primary border element, then the DNS query is responded to withan identification of the primary border element for use by the endpointin registering for the multimedia service.

If the volume of DNS queries is above the threshold capacity of theprimary border element, then a backup border element associated with theend point is determined. If a volume of DNS queries from endpointsassociated with the backup border element is below a threshold capacityof the backup border element, then the DNS query is responded to with anidentification of the backup border element for use by the endpoint inregistering for the multimedia service.

If the volume of DNS queries of the primary border element is above athreshold capacity of the primary border element and if a volume of DNSqueries of the backup border element is above a threshold capacity ofthe backup border element, then the DNS query is responded to with amessage forcing the endpoint to transmit another DNS query at a latertime.

The step of responding to the DNS query with an identification of thebackup border element for use by the endpoint in registering for themultimedia service may further include randomizing a TTL parameter inthe DNS query response to allow reverting of end points to primaryborder elements in a controlled manner.

The DNS server preferably utilizes a standard DNS protocol in receivingand responding to DNS queries. The border elements may be session bordercontrollers. The multimedia service may be a VoIP service. The backupborder element may be a primary border element associated with a secondendpoint.

The identifier of the endpoint may be an IP address. The address of theborder element may be an FQDN.

If the volume of DNS queries is below a threshold capacity of theprimary border element, then the method may further comprise the stepsof receiving at the primary border element a registration request fromthe end point; and transmitting from the primary border element to anetwork registrar a registration request on behalf of the endpoint.

The step of determining a primary border element associated with the endpoint may further include determining a plurality of primary borderelements associated with the end point, and the step of responding tothe DNS query with an identification of a primary border element for useby the endpoint in registering for the multimedia service may beperformed if the volume of DNS queries of any one of the associatedprimary border elements is below a threshold capacity of that primaryborder element.

Another embodiment of the invention is a computer-usable medium havingcomputer readable instructions stored thereon for execution by aprocessor to perform a method for registering a multimedia endpoint viaa border element in a multimedia network as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sequence diagram showing the registration procedure of auser endpoint with a VoIP registrar.

FIG. 2 is a block diagram showing a network configuration as describedin the present disclosure.

FIG. 3 is a schematic diagram of a computer processor according to thepresent disclosure.

FIG. 4 is a flow chart showing a method as described in the presentdisclosure.

DESCRIPTION

The present disclosure describes a mechanism for controlling globalsynchronization, or registration floods, that may result when a largenumber of endpoints in a VoIP network such as an Internet ProtocolMultimedia Subsystem (IMS) come online simultaneously after acatastrophic failure. The catastrophic failure may, for example, be awide-scale power outage, cable cut, or any failure that causes a largenumber of user endpoints to be dropped and that results in thoseendpoint attempting to come on line simultaneously. The mechanismdescribed herein allows the DNS infrastructure to efficiently controlthe overload condition.

The present disclosure describes a mechanism for preventing the messageflood by using a custom DNS infrastructure with added intelligence. Thatmechanism allows some DNS requests to be rejected, and DNS responses tobe modified, effectively distributing the load across a number of borderelements. Furthermore, it manipulates DNS TTL parameters to allowendpoints to gradually revert to their original border elements.

The present disclosure describes modified DNS responses, allowingendpoints to be temporarily assigned to other border elements. Thatscheme further allows the endpoints to automatically revert back totheir originally assigned border elements in a controlled manner.

An example architecture 200 of a system as disclosed herein is shown inFIG. 2. A user endpoint 210 communicates through a network 220, such asthe Internet, with a custom DNS server 224. The user endpoint 210 isalso in communication with a primary border element 232 and/or asecondary or backup border element 233 in a VoIP network 230, asdescribed below. The VoIP network 230 also contains a registrar 234 forregistering user endpoints with border elements.

The custom DNS server 224 may include a processor for executing methodsand steps that are stored on computer-readable media such as ROM or RAMmemory, magnetic memory such as disks or tape, or optical memory. Theprocessor is connected to a bus that communicates with a reader of thecomputer-readable media. The DNS server bus also communicates with inputand output devices such as data storage devices and network interfacesor communications ports for communicating through the network 220.

FIG. 3 illustrates an example computer system 300 for performing thepresently disclosed methods. As shown in FIG. 1, the system 300 includesa computer 310. The computer 310 may be part of a custom DNS server (notshown), or may connected for controlling one or more DNS servers.

The computer 310, which may be a portable or laptop computer or amainframe or other computer configuration, includes a central processingunit (CPU) 325 and a memory 330 connected to an input device 350 such asa keyboard, mouse, drive or network interface and an output device 355such as a display, drive or network interface. The CPU 325 includes aDNS registration software module 345 configured to perform one or moremethods as discussed herein. Although shown inside the CPU 325, themodule 345 can be located outside the CPU 325.

The memory 330 includes a random access memory (RAM) 335 and a read-onlymemory (ROM) 340. The memory 330 can also include a database, diskdrive, tape drive, etc., or a combination thereof. The RAM 335 functionsas a data memory that stores data used during execution of a program inthe CPU 325 and is used as a work area. The ROM 340 functions as aprogram memory for storing a program executed in the CPU 325. Theprogram may reside on the ROM 340 or on any other computer-usable mediumas computer readable instructions stored thereon for execution by theCPU 325 or other processor to perform the methods of the invention. TheROM 340 may also contain data for use by the programs, such as routingdata and DNS parameters.

The input 350 may be a keyboard, mouse, network interface, etc., and theoutput 355 may be a liquid crystal display (LCD), cathode ray tube (CRT)display, printer, etc.

The computer 310 can be configured to operate and display information byusing, e.g., the input 350 and output 355 devices to execute certaintasks. Program inputs may be input through the input 350, may be storedin memory 330, or may be received as live data from the DNS system.

Returning to FIG. 2, the custom DNS server 224 utilizes standard DNSprotocol in implementing the presently described methods. DNS utilizesprimarily User Data Protocol (UDP) to serve requests. A DNS queryincludes a single UDP request from the client followed by a single UDPreply from the server. In implementing the presently described systemsand methods, the DNS server is customized by manipulating parametersused within the standard DNS protocol.

In the system and methods described in the present disclosure, thecustom DNS server 224 is configured with several parameters. First,primary border elements such as element 232 are associated in a databasewith each high-level FQDN. Second, backup border elements such aselement 233 are also associated each of the high-level FQDNs. The backupborder elements may be primary border elements for high-level FQDNs inother geographic locations, that are most likely unaffected by a givencatastrophic failure affecting the subject high-level FQDN. Third, thecustom DNS server 224 is configured to allow only a maximum number ofregistrations to each border element. Thresholds defining those maximamay also be stored in a database.

The custom DNS server 224 maintains a running window of the number ofrequests processed for each border element. If the number of requestsexceeds the assigned capacity or maximum threshold of a primary borderelement, the DNS server modifies subsequent responses to distribute theadditional load across the backup border elements. If the number ofrequests received by the DNS server exceeds the assigned capacity ofboth the primary border element and the backup border elements, the DNSserver responds with a DNS error that forces the client to re-query theDNS server at a later time.

The DNS TTL parameters for responses that specify the backup borderelements are furthermore randomized over a given time window to allowthe endpoints to automatically revert to their normal primary borderelements in a controlled manner, without overwhelming the borderelements. For example, each registration of a UE with a backup borderelement may include a TTL parameter expiring at a random point during adefined future time period. In that way, the primary border elementswill not be overwhelmed as registrations with backup border elementssimultaneously expire. Note that reverting to the primary borderelements would not impact any in-progress calls.

A method in accordance with the present disclosure is represented by theflow chart 400 of FIG. 4. In the method, a multimedia endpoint isregistered via a border element in a multimedia network such as a VoIPnetwork. The method starts at step 410 wherein, at a DNS server in themultimedia network, a DNS query is received from the multimedia userendpoint. The query contains an identifier of the user endpoint andrequests an address of a border element for use in registering for amultimedia service.

Based on the identifier of the end point, a primary border elementassociated with the user endpoint is determined at 420. If a volume ofDNS queries from user endpoints associated with the primary borderelement is below a threshold capacity of the primary border element, asdetermined at 430, then the DNS server responds to the DNS query at 440with an identification of the primary border element for use by theendpoint in registering for the multimedia service.

If, on the other hand, the volume of DNS queries is above a thresholdcapacity of the primary border element, then a secondary or backupborder element associated with the endpoint is determined at 450.

If the volume of DNS queries from endpoints associated with the backupborder element is below a threshold capacity of the backup borderelement, as determined at 460, then the system responds to the DNS queryat 470 with an identification of the backup border element for use bythe endpoint in registering for the multimedia service. If the volume ofDNS queries of the primary border element is above a threshold capacityof the primary border element, and if a volume of DNS queries of thebackup border element is above a threshold capacity of the backup borderelement, then the system responds at 480 to the DNS query with a messageforcing the endpoint to transmit another DNS query at a later time.

The alternative architecture and methods presented herein do not requiremodification of border elements or VoIP user endpoints. The REGISTERmessage flood at the border elements that normally occurs in theaftermath of a catastrophic failure is greatly reduced or completelyavoided. The architecture may be configured to be fully standardscompliant.

The foregoing Detailed Description is to be understood as being in everyrespect illustrative and exemplary, but not restrictive, and the scopeof the invention disclosed herein is not to be determined from theDetailed Description, but rather from the claims as interpretedaccording to the full breadth permitted by the patent laws. Thedescribed embodiments are merely illustrative of the principles of thepresent invention and various modifications may be implemented by thoseskilled in the art without departing from the scope and spirit of theinvention.

What is claimed is:
 1. A method for registering a multimedia endpointvia a border element in a multimedia network, the method comprising: ata domain name system server in the multimedia network, receiving adomain name system query from the multimedia endpoint, the querycontaining an identifier of the multimedia end point and requesting anaddress of a border element for use in registering for a multimediaservice; based on the identifier of the multimedia end point,determining a primary border element associated with the multimedia endpoint; determining that a volume of domain name system queries fromendpoints associated with the primary border element is above athreshold capacity of the primary border element; determining a backupborder element associated with the multimedia end point; determiningthat a volume of domain name system queries from endpoints associatedwith the backup border element is below a threshold capacity of thebackup border element; and responding to the domain name system querywith: an identification of the backup border element for use by themultimedia endpoint in registering for the multimedia service; and arandomized time-to-live parameter for use by the multimedia endpoint inreverting to the primary border element.
 2. The method of claim 1,wherein the time-to-live parameter expires at a random point during apredefined future time period.
 3. The method of claim 1, wherein thedomain name system server utilizes a standard domain name systemprotocol in receiving and responding to domain name system queries. 4.The method of claim 1, wherein the border elements are session bordercontrollers.
 5. The method of claim 1, wherein the multimedia service isa voice-over Internet protocol service.
 6. The method of claim 1,wherein the backup border element is a primary border element associatedwith a second endpoint.
 7. The method of claim 1, wherein the identifierof the multimedia endpoint is an Internet protocol address.
 8. Themethod of claim 1, wherein the address of the border element is a fullyqualified domain name.
 9. The method of claim 1, wherein the methodfurther comprises: receiving at the backup border element a registrationrequest from the multimedia end point; and transmitting from the backupborder element to a network registrar a registration request on behalfof the multimedia endpoint.
 10. The method of claim 1, furthercomprising: at the domain name system server in the multimedia network,after responding to the domain system query, receiving additional domainname system queries from a plurality of multimedia endpoints, thequeries being received at points in time that are randomized over apredefined time period.
 11. A tangible computer-readable medium havingstored thereon computer readable instructions for registering amultimedia endpoint via a border element in a multimedia network,wherein execution of the computer readable instructions by a processorcauses the processor to perform operations comprising: at a domain namesystem server in the multimedia network, receiving a domain name systemquery from the multimedia endpoint, the query containing an identifierof the multimedia end point and requesting an address of a borderelement for use in registering for a multimedia service; based on theidentifier of the multimedia end point, determining a primary borderelement associated with the multimedia end point; determining that avolume of domain name system queries from endpoints associated with theprimary border element is above a threshold capacity of the primaryborder element; determining a backup border element associated with themultimedia end point; determining that a volume of domain name systemqueries from endpoints associated with the backup border element isbelow a threshold capacity of the backup border element; and respondingto the domain name system query with: an identification of the backupborder element for use by the multimedia endpoint in registering for themultimedia service; and a randomized time-to-live parameter for use bythe multimedia endpoint in reverting to the primary border element. 12.The tangible computer-readable medium of claim 11, wherein thetime-to-live parameter expires at a random point during a predefinedfuture time period.
 13. The tangible computer-readable medium of claim11, wherein the domain name system server utilizes a standard domainname system protocol in receiving and responding to domain name systemqueries.
 14. The tangible computer-readable medium of claim 11, whereinthe border elements are session border controllers.
 15. The tangiblecomputer-readable medium of claim 11, wherein the multimedia service isa voice-over Internet protocol service.
 16. The tangiblecomputer-readable medium of claim 11, wherein the backup border elementis a primary border element associated with a second endpoint.
 17. Thetangible computer-readable medium of claim 11, wherein the identifier ofthe multimedia endpoint is an Internet protocol address.
 18. Thetangible computer-readable medium of claim 11, wherein the address ofthe border element is a fully qualified domain name.
 19. The tangiblecomputer-readable medium of claim 11, wherein the operations furthercomprise: at the domain name system server in the multimedia network,after responding to the domain system query, receiving additional domainname system queries from a plurality of multimedia endpoints, thequeries being received at points in time that are randomized over apredefined time period.
 20. A system comprising a processor and atangible computer-readable medium having stored thereon computerreadable instructions for registering a multimedia endpoint via a borderelement in a multimedia network, wherein execution of the computerreadable instructions by the processor causes the system to performoperations comprising: at a domain name system server in the multimedianetwork, receiving a domain name system query from the multimediaendpoint, the query containing an identifier of the multimedia end pointand requesting an address of a border element for use in registering fora multimedia service; based on the identifier of the multimedia endpoint, determining a primary border element associated with themultimedia end point; determining that a volume of domain name systemqueries from endpoints associated with the primary border element isabove a threshold capacity of the primary border element; determining abackup border element associated with the multimedia end point;determining that a volume of domain name system queries from endpointsassociated with the backup border element is below a threshold capacityof the backup border element; and responding to the domain name systemquery with: an identification of the backup border element for use bythe multimedia endpoint in registering for the multimedia service; and arandomized time-to-live parameter for use by the multimedia endpoint inreverting to the primary border element.